Water flows through the tube shown in figure (13-E10). The areas of cross section of the wide and the narrow portions of the tube are 5 cm2 and 2 cm2 respectively. The rate of flow of water through the tube is 500 cm3 s-1. Find the difference of mercury levels in the U-tube.

Let the wider tube be called A and the narrow tube be called B.
Given, area of cross-section of tube A, ![]()
area of cross-section of tube B, ![]()
Rate of flow through the tubes, ![]()
Let the velocity of flow at A and B be 
 and 
 respectively.
From the equation of continuity, we know
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Similarly, ![]()
The pressure difference between the points is equal to the difference in the mercury columns. Let the pressure at A be 
 and that at B be 
. Also, Let the difference in height of the mercury columns be ![]()
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From the Bernoulli’s equation
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